1. Field of the Invention
The present invention relates generally to motor vehicle transmissions and, more particularly, to a torque converter of the type used in automatic transmissions whose torus shape has a reduced axial dimension.
2. Description of the Prior Art
It is well known that torque converters used in automatic transmissions include an impeller which is driven by an engine shaft or the like, a turbine which responds to hydraulic fluid discharged from the impeller, and a stator positioned between the outlet of the turbine and the inlet of the impeller to multiply the torque delivered to the output shaft driving the speed change mechanism of the transmission. These members are disposed in a toroidal chamber. A median section through the toroid illustrates a generally annular flow path through the impeller, the turbine and the stator between outer and inner housings of each component.
The performance of torque converters is conventionally characterized by the ratio of the rotary speed of the turbine to the impeller speed as well as by the impeller input torque. The known hydraulic torque converters are designed as a compromise between an impeller to turbine speed ratio as close as possible to one and a low impeller input torque. To increase the efficiency of the torque converter, a conventional engineering practice has been to maintain the flow volume constant through the flow path by maintaining the product of the diameter of a circle touching the inner and outer walls of the torus and the distance from the center of the circle to the axis of the torus at a constant value. Such design considerations are referred to in U.S. Pat. No. 3,503,209 and S.A.E. design practices exhibited in Jandasek, V. J., THE DESIGN OF A SINGLE-STAGE, THREE-ELEMENT TORQUE CONVERTER, FOR PASSENGER CAR AUTOMATIC TRANSMISSIONS, Volume 1, 1962.
Attempts to depart from this conventional understanding have resulted in torque converter constructions having less efficiency or greater torque losses than may be desirable. For example, U.S. Pat. No. 4,186,557 to Arai et al discloses a turbine modification in torque converters where the torus has a median section with an axial dimension smaller than its dimension in a direction perpendicular to the axis of the torus. The patent addresses the problem of eddy currents through the main passageways in such a construction by maximizing the area of the flow path at the inlet of the turbine and thereafter reducing the torus flow area. While such variations of the flow path volume improve the speed ratio between the impeller and the turbine, such a construction sacrifices the torque available to drive the turbine in the same manner as a reduced volume flow path.